1. Field of Invention
The invention relates to apparatus and methods for suppressing vibrations of an internal combustion engine caused by the cranking of the engine.
2. Description of Related Art
A reciprocating piston engine, that is, a type of internal combustion engine, is started by a cranking operation of turning a crankshaft of the engine via an electric motor. Conventionally, substantially no technical attention has been given to vibrations caused at the time of the cranking of the engine, more precisely, during the cranking thereof. With regard to the vibrations at the time of a start of an engine, Japanese Patent Application Laid-Open No. 10-212983 describes an arrangement in which an engine is cranked by a first electric motor, and at the instant when the engine starts combustion revolution, a drive torque of a second electric motor is applied in a direction opposite to the direction of the drive torque of the first electric motor so as to suppress vibrations caused by sharp changes in torque at the time of the start of combustion revolution. However, this vibration suppressing measure is concerned with vibrations occurring after the cranking ends, and is not concerned with vibrations occurring during the cranking.
In relation to the operation of a vehicle run by a reciprocating piston engine, such as a motor vehicle or the like, a general idea is that the cranking of the engine is performed only at the initiation of each operation of the vehicle, and that once the engine is started, the cranking of the engine is no longer needed as long the engine normally operates, regardless of how long the vehicle continues to be in operation.
However, due to recent needs for fuel resource conservation and environmental protection, great attention has been drawn to fuel-saving vehicles that temporarily stop the engine at the time of temporary vehicle stops for traffic signals or in traffic jams or at the time of slow runs (i.e., slow-speed movement) in heavy traffic during operation of the vehicle. In addition, it is known to provide hybrid vehicles that utilize engine drive and electric motor drive in appropriate combinations in accordance with the state of vehicle running, etc. In the fuel-saving motor vehicles and the hybrid vehicles, the engine is stopped and restarted at various occasions during an operation of the vehicle. Therefore, for further improved noise suppression of such a vehicle, the vibrations of the engine associated with the cranking of the engine need to be suppressed not only after the cranking (as in the aforementioned laid-open patent application), but also during the cranking. However, in the engine described in the aforementioned Japanese Patent Application Laid-Open No. 10-212983, no provision is made for suppressing vibrations that occur during the cranking.